In the first data transmission systems using amplitude modulation, the carrier was recovered at the receiver from a vestigial carrier left in the transmitted signal for this purpose, or from specific pilot frequency signals added to the transmitted signal. However, this wastes the frequency spectrum available and reduces transmission efficiency. Subsequently it was proposed that the carrier should be recovered from particular characteristics of the received and demodulated data signal, without using pilot frequencies or vestigial carriers. Thus, for synchronous digital transmission using single side-band amplitude modulation, it is known to use carrier recovery circuits that use an oscillator controlled by a feedback control circuit tending to cancel the average value of the received and demodulated signals between two consecutive transitions in the same direction, or tending to maximise a component at twice the symbol frequency of the synchronous digital signal, said component being obtained by squaring the received and demodulated signal, or even, tending to make the spacing between odd and even zero passages of the received and demodulated signal equidistant on average. Carrier recovery circuits of the latter type are described in the Assignee's published French patent application No. 7806954 filed on the Mar. 10, 1978 and published under the No. 241 96 14 (corresponding to U.S. Pat. No. 4,253,189). Essentially, these circuits comprise a voltage controlled variable frequency oscillator (VCO) where the control voltage is provided by a sign coincidence auto-correlator operating on the basis of two versions of the received and demodulated signal, one version being delayed relative to the other by an integer multiple of a unit time interval in the synchronous digital signal under consideration. These circuits have the advantage of being constituted principally from circuit elements that operate on an all or nothing basis and which are therefore cheap to embody using the technologies usually used for embodying digital circuits.